Integument
§ Largest organ in human body
§ 15-20% total body weight
I. Functions
A. Sensation- receptor for pain, pressue, touch,temp
B. Conversion- precursor molec into Vit D
C. Regulation- of heat
D. Aborption- of certain lipid soluble therapeutic substances
E. Protection- against injury and prevention of water loss
F. Excretion- of waste products via sweat glands
II. Epidermis
§ Avascular layers of keratinocytic and non-keratinocytic cells
§ Thin skin- hairy skin, most of body
§ Thick skin- hairless skin, palms/soles
A. Keratinocytes
§ Sqamous cells which form a stratified epithelium
§ Major cellular component of epidermis
§ Migrate from basal layer to fuperficial lyaer (3-4 weeks)
B. keratinizing upper region
§ stratum corneum
cornified layer or horny layer
multiple layers of flake like cells killed with keratin, no nuclei or organelles
eventually shed from skin surface
§ stratum lucidum
homogenous eosinphilic zone between stratum corneum and stratum granulosum
only present in thick skin
C. nonkeratinizing lower region (stratum malpighii or malpighiian layer; joined via desmosomes)
§ stratum granulosum
granular layer
1-3 layers of flat cells containing keratohyaline granules
§ stratum spinosum
spinous layer or pricle cell layer
often thickest layer
suprabasal cells are rounder and superficial cells are flatter
§ stratum germinativum
stratum basale/basalis or basal layer
single row of mitotically active columnar to cuboidla cells
give rise to other keratinocyts
D. keratinization
§ basal and spinous cells contain RER, mitoch, golgi, free ribo, tonofilaments (tonofibrils in spinous cells)
§ keratohyaline granules rich in histidine, cystin, and filaggrin (combines with tonofibril in keratinization)
§ cells under go keraitinization after leaving stratum granulosum and enteing stratum corneum
§ keratinization involves breakdown of nucleus and organelles & thickening of plasma membrane
§ keratin- dead cells with thick plasma membranes, ctoplasmic filaments, and interfiamentous matrix
§ keratinization via granules = soft keratn (skin)
§ keratinization without granules = hard keratin (hair and nail)
E. water barrier
§ lipid containing lamellar granules (Oakland bodies) produced by golgi of keratinocytes an discharged into intercellular space by granular layer cells
§ released lipid localized to lower stratum corneum forming a barrier to water loss
F. non-keratinocytic cells
§ melanocytes
round cells with clear cytoplasm, basophilic nuclei, and long dendritic processes
located within basal layer of epidermis but originate in neural crest
do not establish desmosomal attachments
contain premelanosomes which are membrane bound spherical and elliptical organelles produced by golgi
have finely ordered lamellar internal structure which becomes obscured as melanin is produced and deposited.
When fully formed they are called melanosomes, which are transferred to keratinocytes’ cytoplasm via melanocytes’ dendritic processes
Within (pre)melanosomes: tyrosineàDOPA àmelanin (tyrosinase)
Skin color is influenced by:
Melanin: brown-yellow to black pigment within melanosomes
Number of melanocytes in normal skin is constant among races
Degree of skin pigmentation is dependent on number, size, stability, degree of melanization of melanosomes in keratinocytes
Tanning of skin is due to increased melanosome production / increased pigment shields nucleic acid and proteins from UV radiation
Albinism due to absent trosinase activity
Gray hairs due to decrease number and activity of melanocytes in follicular bulbs
Oxyhemmoglobin in dermal vascular bed
Carotenes (food pigment in fat-containing tissues)
Exogenous mineral (tattoos)
Hemoglobin breakdown products
§ langerhan’s cells
located within stratum spinosum,, dermis, lymphoid tissue
contain birbeck granules (tennis racquet)
no desmosomal attachments
immune function- antigen presentation to T-lymphocytes
§ merkel cells
located within stratum germinativum (high concen. In digits, orogenital region, hair follicles)
establishes desmosomal attachments
III. Epidermal-Dermal Junction (EDJ)
§ Epidermis is separated from the dermis by a basal lamina
§ EDJ is composed of : lamina lucida, lamina densa, sublamina densa
§
IV. Dermis
Composed of collagen, elasic fibers, ground subsstance, and fibroblasts
Contains blood and lymphatic vessels, nerve endings, and cutaneious adnexal structures
Also striated muscle fibers in face and neck and smooth muscle fibers in external genitalia and areola
A. papillary dermis
§ more superficial
§ loose CT separated from epidermis by basal lamina
§ incudes dermal papillae and dermal ridges
B. reticular dermis
§ deeper
§ dense CT which is a thicker layer than papillary dermis
§ thickness varies among different regions of the body
§ may contain some adipocytes
V. Nerves
§ Efferent nerve fibers: innervate blood vessels, cutaneous adnexal structures, smooth muscle
§ Free afferent nerve endings: nocieceptors (pain receptors) in epidermis and dermis
§ Encapsulated nerve endings: nerve end organs
A. meissner corpuscle
§ located in dermal papillae, immediatel under epidermis, of palms, soles, digits, nipples, lips
§ cylindrical or pear shaped structure with a zigzag arrangement of unmyelinated termina afferent nerve fibers with supporting (laminar) cellsthought to be schwann cells
§ tactitle recpetor
B. pacinian corpuscle
§ located in deep dermis or subcutis of weight bearing and sensitive areas
§ ovoid stucture which resembles a cut onion and contains terminal affernt nerve fiber with supporting (laminar) cells thought to be schwann cells
Tags: absorption, Albinism, basal cells, basophilic nuclei, Carotenes, collagen, conversion, cytoplasm, dendritic processes, dermis, Epidermal-Dermal Junction, epidermis, Exogenous mineral, exretion, fibroblasts, free ribo, germinativum, golgi, Hemoglobin, homogenous eosinphilic zone, Integument, keratinizing, keratinocytic, lamellar granules, Langerhans cells, malpighii, malpighiian, melanin, melanocytes, mitoch, non-keratinocytic cells, organelles, ovoid stucture, pacinian corpuscle, pigmentation, regulation, sensation, spinous cells, Sqamous cells, stratum granulosum, stratum lucidum, stratum spinosum, tactitle recpetor, tonofilaments
